Epitaxial growth of nitride compound semiconductor

ABSTRACT

The present invention provides materials and structures to reduce dislocation density when growing a III-nitride compound semiconductor. A II-nitride compound single crystal-island layer is included in the semiconductor structure, and III-nitride compound semiconductor layers are to grow thereon. It reduces the dislocation density resulted from the difference between the lattice constants of the GaN compound semiconductor layers and the substrate. It also improves the crystallization property of the III-nitride compound semiconductor.

FIELD OF THE INVENTION

[0001] The present invention provides a III-nitride compoundsemiconductor device, which is characterized by having a II-nitridecompound crystal-island layer in the structure to reduce dislocation ofthe III-nitride compound occurred during epitaxial growth.

BACKGROUND OF THE INVENTION

[0002] III-nitride compound semiconductors, especially semiconductorswith GaN-based material are frequently applied to produce light emittingdevices such as blue-green light emitting diodes (LED) and laser diodes.These materials usually grow on aluminum oxide (Al₂O₃) substrates orsilicon carbide (SiC) substrates.

[0003] Take the aluminum oxide substrates for example. Because thedifference between the lattice constants of Al₂O₃ substrates and GaNexceeds 16%, a GaN crystal layer is hard to directly grow on an Al₂O₃substrate. In U.S. Pat. No. 4,855,249, therefore, Akasaki et al. firstdisclosed to grow an amorphous AlN buffer layer on an Al₂O₃ substrate ata low temperature so as to reduce problem caused by the lattice constantdifference between an Al₂O₃ substrate and a GaN layer. Nakamura et al.,in U.S. Pat. No. 5,290,393, disclosed to use materials such as GaN orAlGaN to grow as a buffer layer. An amorphous GaN buffer layer was firstgrowing on an Al₂O₃ substrate at a temperature between 400° C. and 900°C. A GaN epitaxy layer was then growing on the GaN buffer layer at atemperature between 1000° C. and 1200° C. The quality and performance ofthe GaN epitaxy layer were better than those of a GaN epitaxy layerproduced by adopting AlN as a buffer layer.

[0004] However, because of dislocation defects caused by the differencebetween the lattice contants of Al₂O₃ substrates and GaN materials, evenGaN-based, AlGaN-based or AlN-based materials are provided as bufferlayer materials, epitaxy layer with GaN-based material still has adislocation density of 10¹⁰ cm⁻² to 10⁸ cm⁻². This leads to a badperformance of the semiconductor device and affects illumination andelectrical property. Thus, methods on how to reduce dislocation density,such as multiple buffer layer structure, epitaxy lateral overgrowth(ELOG) structure, InGaN/GaN superlattice structure, or AlGaN/GaNsuprelattice structure, are brought up one after another to reducedislocation.

SUMMARY OF THE INVENTION

[0005] The present invention provides a II-nitride compound material togrow directly on the substrate. This II-nitride compound material growsevenly on the substrate or on the III-nitride compound material withcrystal-island structure. The III-nitride compound semiconductor layeris to grow thereon to reduce dislocation of the III-nitridesemiconductor layer and improve the epitaxy quality.

[0006] The present invention discloses a light emitting device with asingle crystal island structure. The materials of the singlecrystal-island layer are II-nitride compounds, wherein the II-groupelements include beryllium (Be), magnesium (Mg), calcium (Ca), strontium(Sr), barium (Ba), zinc (Zn), cadmium (Cd), and mercury (Hg) etc. Thesingle crystal-island layer grows on the substrate with a certaindistance between each two of the single crystal islands. III-nitridecompound semiconductor layer then grows on the single crystal-islandlayer. Because III-nitride compound semiconductor layer grows alongII-nitride compound single crystal islands, dislocation occurred duringepitaxy is to be confined to where II-nitride compound single crystalisland is. Hence, dislocation density is to be reduced effectively.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007]FIG. 1 illustrates the III-nitride compound semiconductorstructure with the single crystal islands grown from the II-nitridecompounds according to the present invention.

[0008]FIG. 2 illustrates one of the embodiments of the semiconductordevice according to the present invention.

[0009]FIG. 3 illustrates the first embodiment of the light emittingsemiconductor device according to the present invention.

[0010]FIG. 4 illustrates the second embodiment of the light emittingsemiconductor device according to the present invention.

[0011]FIG. 5 illustrates the third embodiment of the light emittingsemiconductor device according to the present invention.

[0012]FIG. 6 illustrates the fourth embodiment of the light emittingsemiconductor device according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0013] The present invention provides a III-nitride compoundsemiconductor device characterized by having at least one II-nitridecompound single crystal-island layer in the structure. This reduces thedislocation of the III-nitride compound occurred during epitaxy.

[0014] According to the present invention, III-V compound semiconductorlayers, such as Al_(x)In_(y)Ga_(1−x−y)N layers (0≦x+y≦1), grow on Al₂O₃substrates, SiC substrates, GaAs substrates or Si substrates by means ofhydride vapor phase epitaxy (HVPE), organometallic vapor phase epitaxy(OMVPE), or molecular beam epitaxy (MBE). The source of Ga is TMGa orTEGa; the source of Al is TMAl or TEAl; the source of In is TMIn orTEIn; the source of N is NH₃ or dimethylhydrazine (DMeNNH₂). P-typedopant is selected from the group consisting of Zn, Cd, Be, Mg, Ca, andBa; N-type dopant is selected from the group consisting of Te, Si, Ge,and Sn. II-group elements are selected from the group consisting of Be,Mg, Ca, Sr, Ba, Zn, Cd, and Hg.

[0015]FIG. 1 illustrates the III-nitride compound semiconductorstructure with the single crystal islands grown from the II-nitridecompounds according to the present invention. Single crystal-islandlayer 2, with the material of II-nitride compound, grows on thesubstrate 1 of Al₂O₃, SiC, GaAs or Si. By adjusting the growingtemperature and the growing time of the II-nitride compound, the numberand the sizes of the single crystal islands in the single crystal-islandlayer 2 may be controlled. If the growing temperature is between 200° C.and 1200° C. and the growing time is between 5 seconds and 30 minutes,the density of the single crystal islands may be controlled to be 10⁷cm⁻² or lower. The number of the islands in the II-nitride compoundsingle crystal-island layer 2 decides the number of dislocation defects,while the sizes of the islands in the II-nitride compound singlecrystal-island layer 2 affect the epitaxy property of the III-nitridecompound semiconductor layer 3. When the II-nitride compound singlecrystal-island layer 2 finishes growing on the wafer, the III-nitridecompound semiconductor layer 3 continues to grow on it. The III-nitridecompound semiconductor layer 3 is to grow along the single crystalislands in the II-nitride compound single crystal-island layer 2, anddislocation is to occur between each two of the single crystal islands.This effectively reduces the number of dislocation defects.

[0016]FIG. 2 illustrates one of the embodiments of the semiconductordevice according to the present invention. First, an additionalIII-nitride compound semiconductor layer 4 grows on the substrate 1.This additional III-nitride compound semiconductor layer 4 has a higherdislocation density. Second, a II-nitride compound single crystal-islandlayer 2 grows on the additional III-nitride compound semiconductor layer4. By adjusting the growing temperature and the growing time of theII-nitride compound single crystal-island layer 2, the number and thesizes of the single crystal islands in the single crystal-island layer 2may be controlled. If the growing temperature is between 200° C. and1200° C. and the growing time is between 5 seconds and 30 minutes, thedensity of the single crystal islands may be controlled to be 10⁷ cm⁻²or lower. The III-nitride compound semiconductor layer 3 then continuesto grow on the II-nitride compound single crystal-island layer 2. Thiseffectively reduces the number of dislocation defects. The advantage ofthis structure is that the III-nitride compound semiconductor layer 3lies on the II-nitride compound single crystal-island layer 2, and itmakes the III-nitride compound semiconductor layer 3 grow more easilyfrom the additional III-nitride compound semiconductor layer 4.Therefore the epitaxy quality of GaN may be improved.

[0017]FIG. 3 and FIG. 4 illustrate two different embodiments of thelight emitting semiconductor device according to the present invention,wherein an additional III-nitride compound semiconductor layer 4 growson the substrate 1 of the semiconductor device shown in FIG. 4. Then-type III-nitride compound semiconductor layer 5 grows on theIII-nitride compound semiconductor layer 3 with the structure of theII-nitride compound single crystal-island layer 2. The n-type dopant ofthe n-type III-nitride compound semiconductor layer 5 is selected fromthe group consisting of SiH₄ and S₂H₆, and the electron carrierconcentration is between 1×10¹⁷ cm⁻³ and 1×10²⁰ cm⁻³. Then, the lightemitting region, with In as the semiconductor compound material, growson the n-type III-nitride compound semiconductor layer 5. The structureof this layer may be double heterostructure, single quantum well, ormulti-quantum well 6. The p-type III-nitride compound semiconductorlayer 7 then grows on the light emitting region and thus completes theLED structure. The dopant of the p-type III-nitride compoundsemiconductor layer 7 is selected from the group consisting of Mg and Znetc., and the hole carrier concentration is between 1×10¹⁷ cm⁻³ and5×10¹⁹ cm⁻³. The forward voltage of the LED is between 3.0 V and 3.4 V,which is about 0.5 V to 1.0 V lower than that of the LED without theII-nitride compound single crystal-island layer 2.

[0018]FIG. 5 and FIG. 6 illustrate another two different embodiments ofthe light emitting semiconductor device according to the presentinvention, wherein an additional III-nitride compound semiconductorlayer 4 grows on the substrate 1 of the semiconductor device shown inFIG. 6. The p-type III-nitride compound semiconductor layer 7 grows onthe III-nitride compound semiconductor layer 3 with the structure of theII-nitride compound single crystal-island layer 2. The dopant of thep-type III-nitride compound semiconductor layer 7 is selected from thegroup consisting of Mg and Zn etc., and the hole carrier concentrationis between 1×10¹⁷ cm⁻³ and 5×10¹⁹ cm⁻³. Then, the light emitting region,with In as the semiconductor compound material, grows on the p-typeIII-nitride compound semiconductor layer 7. The structure of this layermay be double heterostructure, single quantum well, or multi-quantumwell 6. The n-type III-nitride compound semiconductor layer 5 then growson the light emitting region and thus completes the LED structure. Then-type dopant of the n-type III-nitride compound semiconductor layer 5is selected from the group consisting of SiH₄ and S₂H₆, and the electroncarrier concentration is between 1×10¹⁷ cm⁻³ and 1×10²⁰ cm⁻³. Theforward voltage of the LED is between 3.0 V and 3.4 V, which is about0.5 V to 1.0 V lower than that of the LED without the II-nitridecompound single crystal-island layer 2.

[0019] The present invention provides a structure to reduce dislocationdefects of the semiconductor layers. The II-nitride compound singlecrystal-island layer is to grow on the substrate or on the III-Vcompound semiconductor layer to effectively reduce dislocation of theIII-nitride compound semiconductor and to improve the epitaxy quality.

[0020] Following examples show different process coefficients to explainthe spirit of the present invention in detail.

[EXAMPLE 1]

[0021] An epi-ready Al₂O₃ substrate is first placed in a reactor. Thesubstrate is preheated at 1150° C. and then hydrogen gas is introducedto clean the wafer surface for 10 minutes. The temperature is thenlowered to approximately 510° C. The source of Zn is DMZn and the sourceof N is NH₃. Therefore a mixed gas flow of 63 μmol/min of DMZn and7.14×10⁻² mol/min of NH₃ is introduced to the reactor, and a singlecrystal-island layer of ZnN grows on the substrate accordingly. Theaverage diameter of the single crystal islands is about 0.2 μm, and thedensity of the islands is about 10⁷ cm⁻². The temperature is then raisedto 1140° C. and another mixed gas flow of b 5.97×10 ⁻⁵ mol/min of TMGaand 1.34×10⁻¹ mol/min of NH₃ is introduced to the reactor, and itresults in a 2 μm GaN semiconductor layer. According to the Hall effectmeasurement, the mobility is about 650 cm²/V-s, and the carrierconcentration is −2.65×10¹⁶cm⁻³ approximately.

[EXAMPLE 2]

[0022] The epitaxy process of example 2 is similar to that of example 1,wherein DCpMg, as the source of Mg, is substituted for DMZn. Under thegrowing temperature of 600° C., a gas flow of 56 μmol/min of DCpMg isintroduced to the reactor. On the substrate it results in a MgN singlecrystal-island layer in which the average diameter of the single crystalislands is about 0.2 μm. According to the Hall effect measurement, themobility is about 635 cm²/V-s, and the carrier concentration is−2.93×10¹⁶ cm⁻³ approximately.

[EXAMPLE 3]

[0023] The pre-treatment of the Al₂O₃ substrate in example 3 is similarto that in example 1. By adjusting the temperature of the substrate to530° C. and introducing a mixed gas flow of 1.19×10⁻⁵ mol/min of TMGa,5.23×10³¹ ⁶ mol/min of TMAl, and 7.14×10⁻² mol/min of NH₃ to thereactor, about 25 nm of AlGaN semiconductor layer is to grow on thesubstrate. Then turn off the aforementioned mixed gas flow and lower thetemperature to 510° C. Furthermore, introduce another mixed gas flow of63 μmol/min of DMZn and 7.14×10⁻² mol/min of NH₃ to the reactor. Itresults in a single crystal-island layer of ZnN on the AlGaNsemiconductor layer. Now raise the temperature to 1140° C and introducea mixed gas flow of 5.97×10⁻⁵ mol/min of TMGa and 1.34×10⁻¹ mol/min ofNH₃ to the reactor, and 2 μm of undoped GaN semiconductor layer is thenformed thereon. According to the Hall effect measurement, the mobilityis about 715 cm²/V-s, and the carrier concentration is −1.97×10¹⁶ cm⁻³approximately.

[EXAMPLE 4]

[0024] The epitaxy process of example 4 is similar to that of example 3,wherein Et₂Be, as the source of Be, is substituted for DMZn. Byadjusting the growing temperature to 450° C. and introducing a mixed gasflow of 75 μmol/min of Et₂Be and 7.14×10⁻² mol/min of NH₃, a singlecrystal-island layer of BeN is then formed. Upon the singlecrystal-island layer grows the GaN semiconductor layer. According to theHall effect measurement, the mobility is about 630 cm²/V-s, and thecarrier concentration is 3.12×10¹⁶ cm⁻³ approximately.

[EXAMPLE 5]

[0025] Similar to example 1, the ZnN single crystal-island layer and theGaN semiconductor layer grow on the Al₂O₃ substrate. A mixed gas flow of5.97×10⁻⁵ mol/min of TMGa, 1.34×10⁻¹ mol/min of NH₃, and 1.77×10−10mol/min of SiH₄ is introduced to the reactor, and it results in 2.5 μmof n-type GaN semiconductor layer, doped with Si, on top of the GaNsemiconductor layer with the ZnN single crystal-island layer. Then turnoff all the gas flows and lower the temperature of the substrate to 820°C. Introduce another mixed gas flow of 8.61 μmol/min of TMGa, 4.73μmol/min of TMIn, and 0.134 mol/min of NH₃ to the reactor, and itresults in a light emitting region of the multi-quantum well (MQW)structure. Now turn off all the gas flows and raise the temperature ofthe substrate to 1110° C. Introduce the other mixed gas flow of 47.5μmol/min of TMGa, 1.25×10⁷ mol/min of DCpMg, and 8.93×10⁻² mol/min ofNH₃ to the reactor, and 0.5 μm of p-type GaN semiconductor layer, dopedwith Mg, is formed accordingly on the light emitting region of the MQWstructure. The forward voltage of the LED structure is 3.1 V at 20 mA.

[EXAMPLE 6]

[0026] Similar to example 5, the LED structure grows upon the GaNsemiconductor layer with the MgN single crystal-island layer. When madeinto a wafer, the forward voltage is 3.05 V at 20 mA.

[EXAMPLE 7]

[0027] The epitaxy process of example 4 is similar to that of example 3,wherein DMCd, as the source of Cd, is substituted for DMZn. A gas flowof 75 μmol/min of DMCd is introduced to the reactor at the growingtemperature of 680° C., and it results in the GaN semiconductor layerwith the CdN single crystal-island layer. Similar to example 5, the LEDstructure then grows upon the GaN semiconductor layer. When made into awafer, the forward voltage is 3.2 V at 20 mA.

[EXAMPLE 8]

[0028] The pre-treatment of the Al₂O₃ substrate in example 8 is similarto that in example 1. By adjusting the temperature of the substrate to530° C. and introducing a mixed gas flow of 1.02×10⁻⁵ mol/min of TMInand 7.14×10⁻² mol/min of NH₃ to the reactor, crystal-island layer of InNis to grow on the substrate. Then introduce another gas flow of5.23×10⁻⁶ mol/min of TMAl to the reactor, and it results in acrystal-island layer of AlInN. The thickness of these two crystal-islandlayers is 35 nm approximately. Then turn off the TMIn gas whilecontinuing to introduce the TMAl and NH₃ gases, and it results in aAlGaN layer with a thickness of 25 nm. Now turn off the TMAl and NH₃gases and lower the temperature to 510° C. Introduce another mixed gasflow of 63 μmol/min of DMZn and 7.14×10⁻² mol/min of NH₃ to the reactor,and the ZnN single crystal-island layer grows on the AIN layeraccordingly. By raising the temperature to 1000° C. and introducing amixed gas flow of 5.97×10⁻⁵ mol/min of TMGa and 1.34×10⁻¹ mol/min of NH₃to the reactor, 0.5 μm of undoped GaN semiconductor layer is formedthereon. Lower the temperature to 600° C. and introduce a mixed gas flowof 57 μmol/min of DCpMg and 7.14×10⁻² mol/min of NH₃ to the reactor, andit results in a MgN single crystal-island layer on the GaN layer. Againraise the temperature to 1000° C. and introduce a mixed gas flow of5.97×10⁻⁵ mol/min of TMGa and 1.34×10⁻¹ mol/min of NH₃ to the reactor,and 0.5 μm of undoped GaN semiconductor layer is formed accordingly.Raise the temperature of the substrate to 1150° C. and introduce a mixedgas flow of 5.97×10⁻⁵ mol/min of TMGa, 1.34×10⁻¹ mol/min of NH₃, and1.77×10⁻¹⁰ mol/min of SiH₄ to the reactor, and 2.5 μm of n-type GaNsemiconductor layer, doped with Si, is then formed. Now turn off all thegas flows and lower the temperature of the substrate to 820° C. A mixedgas flow of 8.61 μmol/min of TMGa, 4.73 μmol/min of TMIn, and 0.134mol/min of NH₃ is introduced to the reactor to have the light emittingregion with the MQW structure of InGaN/GaN growing. Then turn off allthe gas flows and raise the temperature of the substrate to 1110° C.Introduce another mixed gas flow of 47.5 μmol/min of TMGa, 1.25×10−7mol/min of DCpMg, and 8.93×10⁻² mol/min of NH₃ to the reactor, and 0.5μm of p-type GaN semiconductor layer, doped with Mg, is therefore formedon the light emitting region with the MQW structure. The LED structureis now completed, and the forward voltage is 3.3 V at 20 mA.

[EXAMPLE 9]

[0029] The pre-treatment of the Al₂O₃ substrate in example 9 is similarto that in example 1. By adjusting the temperature of the substrate to530° C. and introducing a mixed gas flow of 1.02×10⁻⁵ mol/min of TMIn,5.23×10⁻⁶ mol/min of TMAl, and 7.14×10⁻² mol/min of NH₃ to the reactor,25 nm of AlInN semiconductor layer is formed on the substrate. Then turnoff the mixed gas flow of TMIn, TMAl, and NH₃, and raise the temperatureto 1050° C. Introduce another mixed gas flow of 5.97×10⁻⁵ mol/min ofTMGa and 1.34×10⁻¹ mol/min of NH₃ to the reactor, and 0.5 μm of undopedGaN semiconductor layer is to grow thereon. Lower the temperature of thesubstrate to 510° C. and introduce a mixed gas flow of 57 μmol/min ofDCpMg and 7.14×10⁻² mol/min of NH₃ to the reactor, and a MgN singlecrystal-island layer is to grow on the GaN layer. Raise the temperatureto 1050° C. and introduce another mixed gas flow of 5.97×10⁻⁵ mol/min ofTMGa and 1.34×10³¹ ¹ mol/min of NH₃ to the reactor, and 0.5 μm ofundoped GaN semiconductor layer is formed. Now raise the temperature to1100° C. and introduce a mixed gas flow of 47.5 μmol/min of TMGa,1.25×10⁻⁷ mol/min of DCpMg, and 8.93×10⁻² mol/min of NH₃ to the reactor,and 3 μm of p-type GaN semiconductor layer, doped with Mg, is formed onthe GaN layer. Turn off all the gas flows and lower the temperature ofthe substrate to 820° C. Another mixed gas flow of 8.61 μmol/min ofTMGa, 4.73 μmol/min of TMIn, and 0.134 mol/min of NH₃ is introduced tothe reactor, and it results in a light emitting region with the MQWstructure of InGaN/GaN. Finally, raise the temperature of the substrateto 1150° C. and introduce a mixed gas flow of 5.97×10⁻⁵ mol/min of TMGa,1.34×10⁻¹ mol/min of NH₃, and 1.77×10⁻¹⁰ mol/min of SiH₄ to the reactor,and 0.5 μm of n-type GaN semiconductor layer, doped with Si, is formedon the light emitting region with the MQW structure. The LED structureis then completed, and the forward voltage is 3.6 V at 20 mA.

[EXAMPLE 10]

[0030] The pre-treatment of the Al₂O₃ substrate in example 10 is similarto that in example 1. By adjusting the temperature of the substrate to530° C. and introducing a mixed gas flow of 63 μmol/min of DMZn and7.14×10⁻² mol/min of NH₃ to the reactor, a ZnN single crystal-islandlayer is to be formed on the substrate. Then introduce another mixed gasflow of 5.23×10⁻⁶ mol/min of TMAl and 7.14×10⁻² mol/min of NH₃ to thereactor, and 25 mn of AIN semiconductor layer is then formed on thesubstrate. Now turn off the mixed gas flow of TMAI and NH₃ , and raisethe temperature to 1050° C. Another mixed gas flow of 5.97×10⁻⁵ mol/minof TMGa and 1.34×10⁻¹ mol/min of NH₃ is introduced to the reactor tohave 0.5 μm of undoped GaN semiconductor layer growing thereon. Raisethe temperature of the substrate to 1150° C. and introduce a mixed gasflow of 5.97×10⁻⁵ mol/min of TMGa, 1.34×10⁻¹ mol/min of NH₃ , and1.77×10⁻¹⁰ mol/min of SiH₄ to the reactor, and it results in 2.5 μm ofn-type GaN semiconductor layer doped with Si. Now turn off all the gasflows and lower the temperature of the substrate to 820° C. A mixed gasflow of 8.61 μmol/min of TMGa, 4.73 μmol/min of TMIn, and 0.134 mol/minof NH₃ is introduced to the reactor to form a light emitting region withthe MQW structure of InGaN/GaN. Finally, turn off all the gas flows andraise the temperature of the substrate to 1110° C. Introduce a mixed gasflow of 47.5 μmol/min of TMGa, 1.25×10⁻⁷ mol/min of DCpMg, and 8.93×10⁻²mol/min of NH₃ to the reactor, and 0.5 μm of p-type GaN semiconductorlayer, doped with Mg, then grows on the light emitting region with theMQW structure. The LED structure is then completed, and the forwardvoltage is 3.3 V at 20 mA.

[EXAMPLE 11]

[0031] The epitaxy process of example 11 is similar to that of example10, wherein Et₂Be, as the source of Be, is substituted for DMZn. Byadjusting the growing temperature to 450° C. and introducing a mixed gasflow of 75 μmol/min of Et₂Be and 7.14×10⁻² mol/min of NH₃ to thereactor, a single crystal-island layer of BeN is then formed. Now growthe LED structure thereon in a way similar to example 10, and theforward voltage is 3.5 V at 20 mA.

[EXAMPLE 12]

[0032] The pre-treatment of the Al₂O₃ substrate in example 12 is similarto that in example 1. By adjusting the temperature of the substrate to530° C. and introducing a mixed gas flow of 1.02×10⁻⁵ mol/min of TMInand 7.14×10² mol/min of NH₃ to the reactor, a InN single crystal-islandlayer is to be formed on the substrate. Then introduce 5.23×10⁻⁶ mol/minof TMAl to the reactor, and a AlInN single crystal-island layer isformed thereon. The thickness of these two layers is about 35 nm. Turnoff the TMAl gas while continuing to introduce of TMAl and NH₃ gases,and 25 nm of AlGaN layer is then formed. Now turn off TMAl and NH₃gases, and lower the temperature to 510° C. Another mixed gas flow of 57μmol/min of DCpMg and 7.14×10⁻² mol/min of NH₃ is introduced to thereactor to have a MgN single crystal-island layer growing on the A1Nlayer. Raise the temperature to 1050° C. and introduce a mixed gas flowof 5.97×10⁻⁵ mol/min of TMGa and 1.34×10⁻¹ mol/min of NH₃ to thereactor, and it results in 0.5 μm of undoped GaN semiconductor layerthereon. Then raise the temperature of the substrate to 1150° C. andintroduce a mixed gas flow of 5.97×10⁻⁵ mol/min of TMGa, 1.34×10⁻¹mol/min of NH₃ , and 1.77×10⁻¹⁰ mol/min of SiH₄ to the reactor, and itresults in 2.5 μm of n-type GaN semiconductor layer doped with Si. Nowturn off all the mixed gas flows and lower the temperature of thesubstrate to 820° C. Another mixed gas flow of 8.61 μmol/min of TMGa,4.73 μmol/min of TMIn, and 0.134 mol/min of NH₃ is introduced to thereactor to form a light emitting region with the MQW structure ofInGaN/GaN. Finally, turn off all the gas flows and raise the temperatureof the substrate to 1110° C. Introduce another mixed gas flow of 47.5μmol/min of TMGa, 1.25×10⁻⁷ mol/min of DCpMg, and 8.93×10⁻² mol/min ofNH₃ to the reactor, and 0.5 μm of p-type GaN semiconductor layer, dopedwith Mg, then grows on the light emitting region with the MQW structure.The LED structure is then completed, and the forward voltage is 3.3 V at20 mA.

[EXAMPLE 13]

[0033] The epitaxy process of example 13 is similar to that of example12, wherein DMCd, as the source of Cd, is substituted for DCpMg. Byadjusting the growing temperature to 680° C. and introducing a gas flowof 75 μmol/min of DMCd to the reactor, a single crystal-island layer ofCdN is then formed. Now grow the LED structure thereon in a way similarto example 12, and the forward voltage is 3.2 V at 20 mA.

[0034] The invention has been described herein in terms of severalpreferred embodiments. Other embodiments of the invention will beapparent to those skilled in the art from consideration of thespecification and practice of the invention. Furthermore, certainterminology has been used for the purposes of descriptive clarity, andnot to limit the present invention. The embodiments and preferredfeatures described above should be considered exemplary, with theinvention being defined by the appended claims.

What is claimed is:
 1. A light emitting semiconductor device,comprising: a substrate; a II-nitride compound single crystal-islandlayer on said substrate; a first III-nitride compound semiconductorlayer on said II-nitride compound single crystal-island layer; aIII-nitride light emitting region on said first III-nitride compoundsemiconductor layer; and a second III-nitride compound semiconductorlayer on said III-nitride light emitting region.
 2. The light emittingsemiconductor device of claim 1, wherein said first III-nitride compoundsemiconductor layer is an n-type III-nitride compound semiconductorlayer; said second III-nitride compound semiconductor layer is a p-typeIII-nitride compound semiconductor layer.
 3. The light emittingsemiconductor device of claim 1, wherein the material of said substrateis selected from a group consisting of Al₂O₃, SiC, Si, and GaAs.
 4. Thelight emitting semiconductor device of claim 1, wherein said II-nitridecompound single crystal-island layer is made of at least one elementselected from a group consisting of Be, Mg, Ca, Sr, Ba, Zn, Cd, and Hg.5. The light emitting semiconductor device of claim 1, wherein thegrowing temperature of said II-nitride compound single crystal-islandlayer is between 200° C. and 1200° C.
 6. The light emittingsemiconductor device of claim 1, wherein said III-nitride compound lightemitting region is a III-nitride compound semiconductor layer consistingof In.
 7. The light emitting semiconductor device of claim 6, whereinthe structure of said III-nitride compound light emitting region isselected from a group consisting of double heterostructure, singlequantum well, and multi-quantum well.
 8. The light emittingsemiconductor device of claim 2, wherein the dopant of said n-typeIII-nitride compound semiconductor layer consists of at least one of thefollowing elements: Te, Si, Ge, and Sn.
 9. The light emittingsemiconductor device of claim 2, wherein the dopant of said p-typeIII-nitride compound semiconductor layer consists of at least one of thefollowing elements: Mg, Zn, and Cd.
 10. The light emitting semiconductordevice of claim 2, wherein said n-type III-nitride compoundsemiconductor layer is Al_(x)In_(y)Ga_(1−x−y)N, 0≦x+y≦1.
 11. The lightemitting semiconductor device of claim 2, wherein said p-typeIII-nitride compound semiconductor layer is Al_(x)In_(y)Ga_(1−x−y)N,0≦x+y≦1.
 12. A light emitting semiconductor device, comprising: asubstrate; a III-nitride compound semiconductor layer on said substrate;a II-nitride compound single crystal-island layer on said III-nitridecompound semiconductor layer; a first III-nitride compound semiconductorlayer on said II-nitride compound single crystal-island layer; aIII-nitride compound light emitting region on said first III-nitridecompound semiconductor layer; and a second III-nitride compoundsemiconductor layer on said III-nitride compound light emitting region.13. The light emitting semiconductor device of claim 12, wherein saidfirst III-nitride compound semiconductor layer is an n-type III-nitridecompound semiconductor layer; said second III-nitride compoundsemiconductor layer is a p-type III-nitride compound semiconductorlayer.
 14. The light emitting semiconductor device of claim 12, whereinthe material of said substrate is selected from a group consisting ofAl₂O₃, SiC, Si, and GaAs.
 15. The light emitting semiconductor device ofclaim 12, wherein said II-nitride compound single crystal-island layeris made of at least one element selected from a group consisting of Be,Mg, Ca, Sr, Ba, Zn, Cd, and Hg.
 16. The light emitting semiconductordevice of claim 12, wherein the growing temperature of said II-nitridecompound single crystal-island layer is between 200° C. and 1200° C. 17.The light emitting semiconductor device of claim 12, wherein saidIII-nitride compound semiconductor layer is Al_(x)In_(y)Ga_(1−x−y)N,0≦x+y≦1.
 18. The light emitting semiconductor device of claim 12,wherein said III-nitride compound light emitting region is a III-nitridecompound semiconductor layer consisting of In.
 19. The light emittingsemiconductor device of claim 18, wherein the structure of saidIII-nitride compound light emitting region is selected from a groupconsisting of double heterostructure, single quantum well, andmulti-quantum well.
 20. The light emitting semiconductor device of claim13, wherein the dopant of said n-type III-nitride compound semiconductorlayer consists of at least one of the following elements: Te, Si, Ge,and Sn.
 21. The light emitting semiconductor device of claim 13, whereinthe dopant of said p-type III-nitride compound semiconductor layerconsists of at least one of the following elements: Mg, Zn, and Cd. 22.The light emitting semiconductor device of claim 13, wherein said n-typeIII-nitride compound semiconductor layer is Al_(x)In_(y)Ga_(1−x−y)N,0≦x+y≦1.
 23. The light emitting semiconductor device of claim 13,wherein said p-type III-nitride compound semiconductor layer isAl_(x)In_(y)Ga_(1−x−y)N, 0≦x+y≦1.